Frequency modulation MEMS triaxial gyroscope

ABSTRACT

A frequency modulation MEMS triaxial gyroscope, having two mobile masses; a first and a second driving body coupled to the mobile masses through elastic elements rigid in a first direction and compliant in a second direction transverse to the first direction; and a third and a fourth driving body coupled to the mobile masses through elastic elements rigid in the second direction and compliant in the first direction. A first and a second driving element are coupled to the first and second driving bodies for causing the mobile masses to translate in the first direction in phase opposition. A third and a fourth driving element are coupled to the third and fourth driving bodies for causing the mobile masses to translate in the second direction and in phase opposition. An out-of-plane driving element is coupled to the first and second mobile masses for causing a translation in a third direction, in phase opposition. Movement-sensing electrodes generate frequency signals as a function of external angular velocities.

BACKGROUND Technical Field

The present disclosure relates to a frequency modulation MEMS triaxialgyroscope.

Description of the Related Art

As is known, integrated gyroscopes of semiconductor material, obtainedusing MEMS (Micro-Electro-Mechanical Systems) technology, operate on thebasis of the relative-acceleration theorem, exploiting the Coriolisacceleration. In particular, when a linear velocity is applied to amobile mass (also called “proof mass”) rotating at an approximatelyconstant angular velocity, the mobile mass “feels” an apparent force,called Coriolis force, which determines a displacement thereof in aperpendicular direction to the linear velocity and to the rotation axis.By detecting this displacement in the direction of the apparent force,it is thus possible to indirectly measure the angular velocity.

Proposed MEMS gyroscopes work on the basis of two different principles:amplitude modulation and frequency modulation.

In amplitude-modulation gyroscopes, the amplitude of the displacement ofthe mobile mass is measured in a perpendicular direction to the drivingdirection, i.e., the direction of a pre-set linear velocity as imposedon the mobile mass. In particular, in this type of gyroscope, a mobilemass, rotating at an approximately constant velocity about a firstCartesian axis (for example, axis Z of a Cartesian reference system), isdriven in a driving direction (for example, parallel to the axis X). Inthis situation, the Coriolis force causes a displacement in a sensingdirection perpendicular to the previous two directions, for example hereparallel to axis Y. The displacement in the sensing direction isproportional to the amplitude of the driving movement, which is known,and to the external angular velocity, which may thus be determined bymeasuring the displacement.

In frequency modulation gyroscopes of a QFM (quadrature frequencymodulation) type and of an LFM (Lissajous frequency modulation) type thevariation of frequency due to the Coriolis force is measured.

For a deeper understanding of the above, reference may be made to anideal frequency modulation gyroscope of a QFM type for measuring theangular velocity component about the axis Z. In this case, a mobileinertial body of mass m is connected to the substrate by a spring systemhaving stiffnesses k_(x) and k_(y) and allowing translation in the twodirections X and Y and is driven in the two directions of the plane Xand Y.

Assuming, for simplicity, the body as being point-like and neglectingany friction, the equations of motion in an inertial system, projectedin the two directions, as a result of forces F_(x) and F_(y) acting,respectively, along the axis X and the axis Y, are:m{umlaut over (x)}+k _(x) x=F _(x)mÿ+k _(y) y=F _(y)

The natural frequencies of oscillation ω_(ox) and ω_(oy) in the twodirections are:

$\omega_{ox} = \sqrt{\frac{k_{x}}{m}}$$\omega_{oy} = \sqrt{\frac{k_{y}}{m}}$

If ω_(ox)=ω_(oy), the resonance motion is circular, as required byoperation of a QFM type.

In presence of an external angular velocity Ω_(z) (which is assumed asvarying in a negligible way within the measurement interval), theequations are modified as a result of the presence of the Coriolis forceand become:m{umlaut over (x)}−2mΩ _(z) {dot over (y)}+k _(x) x=F _(x)mÿ+2mΩ _(z) {dot over (x)}+k _(y) y=F _(y)  [1]where the terms 2mΩ_(z){dot over (y)} and 2mΩ_(z){dot over (x)} are dueto the Coriolis forces, and thus the motion changes. In particular, thefrequencies become ω_(x) and ω_(y) and the solution in the idealsimplest case may be expressed in the form:x=xe ^(i(ω) ^(x) ^(t+ψ) ^(x) ⁾y=ye ^(i(ω) ^(y) ^(t+ψ) ^(y) ⁾where ψ_(x) and ψ_(y) are the phases, and x and y are the amplitudesalong the axis X and the axis Y, respectively.

With QFM type operation a phase shift of 90° is imposed between the twodirections (ω_(x)t−ω_(y)t+ψ_(x)−ψ_(y)=90°). Substituting Eqs. [2] in Eq.[1] and considering the forcing term in quadrature with thedisplacement, the real part of the equations yields:

$\begin{matrix}{{{\omega_{x}^{2} + {2\;\Omega_{z}\frac{\overset{\_}{y}\omega_{y}}{\overset{\_}{x}\omega_{x}}\omega_{x}} - \omega_{ox}^{2}} = 0}{{\omega_{y}^{2} + {2\;\Omega_{z}\frac{\overset{\_}{x}\omega_{x}}{\overset{\_}{y}\omega_{y}}\omega_{y}} - \omega_{oy}^{2}} = 0}} & \lbrack 3\rbrack\end{matrix}$

Imposing the constraint yω_(y)=xω_(x) (the quantities yω_(y) and xω_(x)will be also denoted hereinafter as v_(ya) and v_(xa), respectively, inso far as they represent the amplitudes of the oscillation velocities inthe two directions) necessary for the QFM operation considered here, andsolving Eqs. [3] as a function of ω_(x) and ω_(y), we obtain:ω_(x)−ω_(ox)=−Ω_(z)ω_(y)−ω_(oy)=−Ω_(z)by neglecting less influent terms.

Frequency variation measurement consequently enables measurement of theangular velocity Ω_(z).

For a triaxial gyroscope (once again on the ideality hypothesesmentioned above), the inertial body is free to translate with respect tothe substrate in the three directions. In presence of external angularvelocities of components Ω_(x), Ω_(y), Ω_(z), the equations may bewritten as:m{umlaut over (x)}−2mΩ _(z) {dot over (y)}+2mΩ _(y) ż+k _(x) x=F _(x)mÿ−2mΩ _(z) {dot over (x)}+2mΩ _(x) ż+k _(y) y=F _(y)m{umlaut over (z)}−2mΩ _(x) {dot over (y)}+2mΩ _(y) {dot over (x)}+k_(z) z=F _(z)  [4]

Imposing, during operation, the relationyω_(y)=v_(ya)=v_(xa)=xω_(x)=zω_(z)=v_(az), we obtain the followingexpressions that enable measurement of the angular velocity:ω_(x)−ω_(ox)=−Ω_(z)(ϕ_(xy))+Ω_(y) sin(ϕ_(xz))ω_(y)−ω_(oy)=−Ω_(z)(ϕ_(xy))−Ω_(x) sin(ϕ_(yz))ω_(z)−ω_(oz)=+Ω_(y)(ϕ_(xz))−Ω_(x) sin(ϕ_(yz))where ϕ_(xy), ϕ_(xz), and ϕ_(yz) are the phase differences between thedisplacements in parallel directions to the axes appearing in thesubscripts, which may possibly be variable in time (LFM operation). Thenon-idealities of the system (dampings, mechanical couplings on thestiffnesses, variations in time of the amplitude of the displacements)may be included in the system with some degree of formal complicationand will be included in the complete equations of the triaxial gyroscopedescribed hereinafter.

A uniaxial gyroscope operating with frequency modulation is described,for example, in WO 2014/093727. The structure presented therein is verysimple, comprising a single mobile mass, and enables non-differentialmeasurement of the angular velocity acting only along one axis (axis Z).

Another known structure that exploits the principle of frequencymodulation for measurement of the angular velocity is described in thepaper “A 7 ppm, 6°/Hr frequency-output MEMS gyroscope” by Izyumin I., etal., MEMS 2015, Portugal, January 18-22, 2015. In this case, reading theangular velocity acting along the axis Z is differential thanks to theintroduction of four appropriately connected masses. This structure thushas large overall dimensions.

On the other hand, MEMS gyroscopes operating according to the frequencymodulation principle have the advantage of a high stability, and theirsensitivity is less subject to drifts in presence of temperaturevariations, stresses, or over time, as compared to amplitude-modulation(AM) gyroscopes.

BRIEF SUMMARY

According to the present disclosure, a frequency modulation MEMStriaxial gyroscope and the corresponding control method are provided. Inparticular, a MEMS gyroscope operating according to a frequencymodulation principle that is able to detect angular velocities aboutdifferent axes, with a simple and compact structure.

The present disclosure is also directed to MEMS triaxial gyroscope on asubstrate having a first mobile and a second mobile mass suspended overthe substrate and first, second, third, and fourth elastic elements. Thegyroscope includes a first driving body coupled to the first mobile massthrough the first elastic elements, a second driving body coupled to thesecond mobile mass through the second elastic elements, the first andsecond elastic elements being rigid in a first direction and compliantin a second direction transverse to the first direction, a third drivingbody coupled to the first mobile mass through the third elasticelements, and a fourth driving body coupled to the second mobile massthrough the fourth elastic elements, the third and fourth elasticelements being rigid in the second direction and compliant in the firstdirection. The gyroscope also includes a first and a second drivingelement, coupled to the first and second driving bodies, respectively,and configured to cause the first and second mobile masses to translatein the first direction at a first frequency and in phase opposition, athird and a fourth driving element, coupled to the third and fourthdriving bodies, respectively, and configured to cause the first andsecond mobile masses to translate in the second direction at a secondfrequency and in phase opposition, an out-of-plane driving element,coupled to the first and second mobile masses and configured to causethe first and second mobile masses to translate in a third direction, ata third frequency and in phase opposition, the third direction beingtransverse to the first and second directions, and movement sensingelectrodes coupled to the first and second masses in the first, second,and third directions configured to sense movements due to externalangular velocities, and generate, in use, signals at a frequencydepending upon the external angular velocities.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure, a preferredembodiment thereof is now described, purely by way of non-limitingexample, with reference to the attached drawings, wherein:

FIG. 1 is a schematic top plan view of a possible embodiment of thepresent gyroscope;

FIG. 2 shows the deformations undergone by the gyroscope of FIG. 1, as aresult of driving in a first direction;

FIG. 3 shows the deformations undergone by the gyroscope of FIG. 1, as aresult of driving in a second direction;

FIG. 4 is a schematic representation in side view of the gyroscope ofFIG. 1, as a result of driving in a third direction;

FIG. 5 is a top plan view of a fourth possible implementation of thegyroscope of FIG. 1;

FIGS. 6-8 show enlarged details of the structure of FIG. 5;

FIG. 9 shows a simplified block diagram of an electronic apparatusincorporating the gyroscope of FIG. 1; and

FIG. 10 is a top plan view of a portion of a different implementation ofthe gyroscope of FIG. 1.

DETAILED DESCRIPTION

The triaxial gyroscope described herein is based on the solution of theclassic equations of motion that describe a system with three degrees offreedom (triaxial gyroscope) via the method of phasors. These equations,for the ideal case, are represented by Eqs. [4].

Provided hereinafter are the equations of motion in Cartesianco-ordinates for a non-ideal system provided with dampings, stiffnesscouplings k_(xy), k_(xz) and k_(yz) between the various directions, andnon-point-like mass:m{umlaut over (x)}+b _(x) {dot over (x)}+b _(xy) {dot over (y)}+b _(xz)ż−2mα _(z)Ω_(z) {dot over (y)}+2mα _(y)Ω_(y) ż+k _(x) x+k _(xy) y+k_(xz) z−mα _(z) ²Ω_(z) ² x+−mα _(y) ²Ω_(y) ² x+mα _(x)Ω_(x)α_(z)Ω_(z)z+mα _(x)Ω_(x)α_(y)Ω_(y) y−mα _(z){dot over (Ω)}_(z) y+mα _(y){dot over(Ω)}_(y) z−F _(xc) e ^(iΦ) ^(x) −iF _(xs) e ^(iΦ) ^(x) =0,mÿ+b _(y) {dot over (y)}+b _(yz) {dot over (x)}+b _(yz) ż−2mα _(x)Ω_(x)ż+2mα _(z)Ω_(z) {dot over (x)}+k _(y) y+k _(yx) x+k _(yz) z−mα _(z)²Ω_(z) ² y+−mα _(x) ²Ω_(x) ² y+mα _(x)Ω_(x)α_(y)Ω_(y) x+mα_(z)Ω_(z)α_(y)Ω_(y) z−mα _(z){dot over (Ω)}_(z) x−mα _(x){dot over(Ω)}_(x) z−F _(yc) e ^(iΦ) ^(y) −iF _(ys) e ^(iΦ) ^(y) =0,m{umlaut over (z)}+b _(z) ż+b _(zy) {dot over (y)}+b _(zx) {dot over(x)}−2mα _(y)Ω_(y) {dot over (x)}+2mα _(x)Ω_(x) {dot over (y)}+k _(z)z+k _(zy) y+k _(zx) x−mα _(x) ²Ω_(x) ² z+−mα _(y) ²Ω_(y) ² z+mα_(y)Ω_(y)α_(z)Ω_(z) y+mα _(x)Ω_(x)α_(z)Ω_(z) x−mα _(y){dot over (Ω)}_(y)x+mα _(x){dot over (Ω)}_(x) y−F _(zc) e ^(iΦ) ^(z) −iF _(zs) e ^(iΦ)^(z) =0,

On appropriate hypotheses (discussed in detail in the aforementionedinternational patent WO 2014/093727 for the one-axial case), by solvingthe previous equations of motion and imposing a time-dependent phasedifference between the various axes (LFM), the following expressions areobtained:

$\begin{matrix}{{\omega_{x} = {\omega_{ox} - {\alpha_{z}\Omega_{z}\frac{v_{ya}}{v_{xa}}{\sin\left( \phi_{xy} \right)}} + {\alpha_{y}\Omega_{y}\frac{v_{za}}{v_{xa}}{\sin\left( \phi_{xz} \right)}}}},{\omega_{y} = {\omega_{oy} - {\alpha_{z}\Omega_{z}\frac{v_{xa}}{v_{ya}}{\sin\left( \phi_{xy} \right)}} - {\alpha_{x}\Omega_{x}\frac{v_{za}}{v_{ya}}{\sin\left( \phi_{yz} \right)}}}},{\omega_{z} = {\omega_{oz} + {\alpha_{y}\Omega_{y}\frac{v_{xa}}{v_{za}}{\sin\left( \phi_{xz} \right)}} - {\alpha_{x}\Omega_{x}\frac{v_{ya}}{v_{za}}{\sin\left( \phi_{yz} \right)}}}},} & \lbrack 5\rbrack\end{matrix}$where ω_(x), ω_(y) and ω_(z) are the pulsations measured with respect toaxes X, Y and Z, respectively, ω_(0x), ω_(0y), and ω_(0z) are thenatural pulsations, in the absence of the Coriolis force, of the systemwith three degrees of freedom, α_(x), α_(y), and α_(z) are factors thatdepend upon coupling of the modal masses via the Coriolis force (angulargain) and that, in the ideal case of point-like mass, are equal to one,v_(ya), v_(xa), v_(za) have the same meaning indicated above withreference to Eqs. [3], Ω_(x), Ω_(y), and Ω_(z) are the external angularvelocities about the axes X, Y and Z to be determined, and ϕ_(xy),ϕ_(xz), and ϕ_(yz) are the phase differences between the displacementsin the two directions indicated as subscripts.

The pulsations, and thus the frequencies of rotation about the threeaxes, depend upon the external angular velocities. Consequently, througha combined reading of the frequency variation on the three axes, it iseasily possible to derive the value of the sought external angularvelocity.

The present gyroscope has a structure with two (differential) mobilemasses, where each mobile mass may perform pure translations along thethree axes X, Y, and Z, uncoupled from one another, as explainedhereinafter with reference to FIG. 1.

FIG. 1 shows a gyroscope 10 formed by a first mobile mass 11A and by asecond mobile mass 11B.

The mobile masses 11A, 11B are symmetrical with respect to a first andto a second symmetry axis S1, S2, perpendicular to one another andparallel to axes X and Y of a Cartesian reference system XYZ. In thegyroscope 10, the mobile masses 11A, 11B may be translated parallel tothe first and to the second symmetry axis S1, S2, i.e., to the Cartesianaxes X, Y, as well as parallel to a vertical axis O, parallel to axis Zof the Cartesian reference system XYZ and passing through the centroidof the gyroscope 10. Further, in use, the gyroscope 10 is rotatableabout Cartesian axes X, Y, and Z with an angular velocity to bedetermined.

The mobile masses 11A, 11B are coupled together through a central bridgestructure 12. Further, each mobile mass 11A, 11B is suspended over asubstrate 15 (represented only schematically) through anchoringstructures 13, 45A, 45B, 46A, 46B, 47A, 47B and three pairs ofcoupling/driving structures 14A, 14B, 15A, 15B, 16A, 16B, which enable athree-dimensional translational movement, independent in the threedirections, of the mobile masses 11A, 11B, as described in detailhereinafter.

The mobile masses 11A, 11B, the central bridge structure 12, and thecoupling and driving structures 14A, 14B, 15A, 15B, 16A, 16B are formedin a same structural layer, for example of polycrystalline silicon, viasurface micromachining techniques. For example, they are obtained byremoving an underlying sacrificial layer.

In detail, each mobile mass 11A, 11B has a generally rectangular shape,of a thickness (in a direction parallel to axis Z) much smaller than theother dimensions, in a per se known manner. Each mobile mass 11A, 11Bthus has (in top plan view) a first side 20 parallel to axis Y coupledto the central bridge structure 12 (thus, also referred to hereinafteras inner side), a second side 21, opposite to the first side 20,likewise parallel to axis Y, arranged facing outwards (thus, alsoreferred to hereinafter as outer side), and a third side 22 and a fourthside 23 (also referred to hereinafter as top side and bottom side) whichare parallel, in top view, to axis X.

The second, third, and fourth sides 21-23 of the mobile masses 11A, 11Bare each coupled to a respective coupling and driving structure 14A,14B, 15A, 15B, 16A, 16B.

In the embodiment shown, the central bridge structure 12 is formed by across-shaped joint comprising a pair of first bars 25, a second bar 26,and first, second, third, and fourth central springs 27-30.

The first bars 25 extend parallel to axis Y as a prosecution of oneanother and have a longitudinal axis coinciding with the second symmetryaxis S2. The first bars 25 are connected together at an inner endthrough the first central springs 27 and through the second bar 26 andare anchored to the substrate 15 at an outer end through the secondcentral springs 28 and the anchoring structures 13.

The first central springs 27 connect the inner end of the first bars 25to a central portion of the second bar 26 and are substantially flexuresprings that enable rotation of the second bar 26 with respect to thefirst bars 25 about the vertical axis O of the gyroscope 10, but aresubstantially rigid in the other directions. They thus form articulatedjoints of a hinge type, as discussed in detail hereinafter.

The second central springs 28 are torsion springs, which enable rotationof the first bars 25 about the second symmetry axis S2. They may furtherenable a minor rotation of the first bars 25 also about vertical axis Oconcordant, but in general not rigid with respect to, the second bar 26,as explained in greater detail hereinafter.

The third central springs 29 are each arranged between a respective endof the second bar 26 and a respective mobile mass 11A, 11B. The centralsprings 29 are deformable in a direction parallel to axis X (as shown inFIG. 2) so as to uncouple the mobile masses 11A, 11B from the second bar26 (and thus from the first bars 25) in a direction parallel to axis X.The third central springs 29 also enable a rotation of the second bar 26with respect to the mobile masses 11A, 11B, as described hereinafterwith reference to FIG. 3.

The fourth central springs 30 extend between the first bars 25 and thesuspended masses 11A, 11B and are compliant in all three movementdirections of the mobile masses 11A, 11B, parallel to the Cartesian axesX, Y, and Z.

The coupling/driving structures 14A, 14B, 15A, 15B, 16A, 16B are similarto each other and have the task of driving the mobile masses 11A, 11B ina respective direction (parallel to axis X or Y), enabling alsodisplacement thereof parallel to axis Z. Each coupling/driving structure14A, 14B, 15A, 15B, 16A, 16B comprises a respective frame element 31A,31B, 32A, 32B, 33A, 33B, at least one anchoring spring 36A, 36B, 37A,37B, 38A, 38B, and at least one decoupling spring 41A, 41B, 42A, 42B,43A, 43B.

Due to the symmetry of the structure of the gyroscope 10 with respect tothe symmetry axis S2, these structures are identified by a same numberand by the letter A or B, according to whether they are coupled to thefirst mobile mass 11A or to the second mobile mass 11B. Further,hereinafter, where the letters A and B are not indicated, it isunderstood that what is described refers to both the coupling/drivingstructures and to both the elements thereof arranged symmetrically withrespect to the second symmetry axis.

In detail, the frame elements 31-33 (referred to also as X frameelements 31, first Y frame elements 32, and second Y frame elements 33)are here formed by rectangular frames, extending parallel to theCartesian axes X and Y and coupled to respective X coupling/drivingstructures 14, first Y coupling/driving structures 15 and second Ycoupling/driving structures 16.

The X coupling/driving structure 14A, 14B is arranged between the outerside 21 of the respective mobile mass 11A, 11B and second anchoringstructures 45A, 45B and is coupled to respective X anchoring springs 36and respective X decoupling springs 41. Each anchoring spring 36A, 36Bof the X coupling/driving structures 14A, 14B, arranged between therespective second anchoring structures 45A, 45B and the respective Xframe element 31A, 31B, only enables translation of the latter parallelto axis X. Each X decoupling spring 41A, 41B, arranged between therespective X frame element 31A, 31B and the respective mobile mass 11A,11B, enables movements parallel to axes Y and Z of the respective mobilemass 11A, 11B with respect to its own X frame element 31A, 31B, but isrigid parallel to axis X so as to transmit the movements along thisaxis, as explained hereinafter with reference to FIG. 2.

Likewise, the first Y coupling/driving structure 15A, 15B is arrangedbetween the top side 22 of each mobile mass 11A, 11B and a thirdanchoring structure 46A, 46B and is coupled to respective Y anchoringsprings 37 and respective Y decoupling springs 42. The second Ycoupling/driving structure 16A, 16B is arranged between the bottom side23 of each mobile mass 11A, 11B and a fourth anchoring structure 47A,47B and is coupled to respective second Y anchoring springs 38 andrespective second Y decoupling springs 43. Each anchoring spring 37A,37B, 38A, 38B of the second and third Y coupling/driving structures 15A,15B, 16A, 16B, arranged between the respective anchoring structure 46A,46B, 47A, 47B and the respective Y frame element 32A, 32B, 33A, 33B,enables only translation of the latter parallel to axis Y. Each Ydecoupling spring 42A, 42B, 43A, 43B, arranged between the respectiveframe element 32A, 32B, 33A, 33B and the respective mobile mass 11A,11B, enables movements of the latter with respect to its own Y frameelement 32A, 32B, 33A, 33B parallel to axes X and Z, but is rigid in adirection parallel to axis Y so as to transmit movements in thisdirection, as explained hereinafter with reference to FIG. 3.

Hereinafter, the movements of the mobile masses 11A, 11B are describedseparately in the three directions parallel to axes X, Y, and Z (alsoreferred to below as X, Y, and Z movements). However, during operationas triaxial gyroscope, normally the gyroscope is driven in all threedirections simultaneously, and the movements described below add up. Inparticular, the frame elements 31-33 and the mobile masses 11A, 11B maybe driven simultaneously (through the respective driving electrodesdescribed below) with the same amplitude of velocity and appropriatephase to obtain an overall movement of the mobile masses 11A, 11B of athree-dimensional type with three-dimensional Lissajous trajectories inthe LFM case.

In a way not shown in FIG. 1, the X coupling/driving structures 14A, 14Bhave first driving units to translate the mobile masses 11A, 11Bparallel to axis X, in phase opposition, as shown in FIG. 2 (Xmovement). Here, the mobile masses 11A, 11B and the X frame elements31A, 31B are shown in a first position with a solid line and in a secondposition with a dashed line. In particular, the X movement is driven (inthe opposite direction) by the X frame elements 31A, 31B through the Xdecoupling springs 41A, 41B, which are rigid in a direction parallel toaxis X. Thus, as shown by the pair of arrows 50A, 50B in FIG. 2 (whereofa first arrow 50A indicates the X movement in a first step, and a secondarrow 50B indicates the movement in the same direction X in a secondstep), the mobile masses 11A, 11B are driven periodically according tothe differential movement parallel to axis X, which, in the absence ofan external angular velocity, is at the frequency ω_(0x), alwaystogether, moving away from or towards the central bridge structure 12.During the X movement, the X anchoring springs 36A, 36B of the Xcoupling/driving structures 14A, 14B are compressed and the thirdcentral springs 29 expand (and vice versa) on the basis of the drivingphase.

As indicated, during the X movement, since the X decoupling springs 41A,41B of the X coupling/driving structures 14A, 14B are rigid in thedirection parallel to the axis X, they transmit the driving movementfrom the X frame elements 31A, 31B to the respective mobile masses 11A,11B. Further, the Y decoupling springs 42, 43 of the Y coupling/drivingstructures 15, 16 undergo deformation, decoupling the mobile masses 11A,11B from the Y frame elements 32, 33. The third and fourth centralsprings 29, 30 further decouple the mobile masses 11A, 11B from thefirst bars 25 in a direction parallel to the axis X.

Likewise, in a way not shown in FIG. 1, the Y coupling/drivingstructures 15, 16 are provided with second driving units such as togovern movement of the mobile masses 11A, 11B in phase opposition,parallel to the axis Y (Y movement), as shown in FIG. 3. Here, themobile masses 11A, 11B and the Y frame elements 32A, 32B, 33A, 33B areshown in a first position with a solid line and in a second positionwith a dashed line. In particular, the Y movement is driven (in oppositedirections) by the Y frame elements 32A, 32B, 33A, 33B through the Ydecoupling springs 42A, 42B, 43A, 43B, rigid parallel to axis Y. Thus,as shown by the arrows 52A, 52B in FIG. 3 (where a first arrow 52Aindicates the Y movement in a first step, and a second arrow 52Bindicates the Y movement in a second step), the mobile masses 11A, 11Bare driven in an opposite way, one upwards and the other downwards andvice versa according to the movement that, in the absence of an externalangular velocity, has a frequency ω_(0y).

During the Y movement, the Y anchoring springs 37, 38 of the Ycoupling/driving structures 15, 16 compress and expand on the basis ofthe driving phase, whereas the Y decoupling springs 42, 43, rigidparallel to axis Y, transmit the driving movement from the Y frameelements 32, 33 to the respective mobile masses 11A, 11B. In thisdriving mode, the X decoupling springs 41 of the X coupling/drivingstructures 14, as well as the central springs 27, 29 and 30, undergodeformation. Further, as shown in FIG. 3, the second bar 26 turns aboutthe vertical axis O because of the first central springs 27, which inpractice form articulated joints. As indicated above, in this step, alsothe first bars 25 may turn about the vertical axis O, even though to alesser extent than the second bar 26. Alternatively, the first bars 25and the second bar 26 could form a rigid body, rotating together.

The mobile masses 11A, 11B of the gyroscope 10 are further able totranslate parallel to axis Z and uncoupled with respect to the frameelements 31-33 (Z movement). In detail, as shown in FIG. 4, Z drivingelectrodes 68 are provided underneath the mobile masses 11A so as todrive movement thereof in phase opposition, parallel to the axis Z. Inthe example shown in FIG. 4, the Z driving electrodes 68 are formed bydoped regions in the substrate 15, but other solutions are possible.

In use, the Z driving electrodes 68 are biased so as to control movementof the mobile masses 11A, 11B in phase opposition, as shown by arrows54A, 54B (where a first arrow 54A indicates the movement in a firststep, and a second arrow 54B indicates the movement in a second step ofthe Z movement). In practice, the mobile masses 11A, 11B are driven oneaway from and the other towards the substrate 15, and vice versa,according to the movement that, in the absence of an external angularvelocity, has a frequency ω_(0z). During this movement, the decouplingsprings 41-43 (whereof FIG. 4 only shows the decoupling springs 41A,41B, 42A, 42B), the second, third, and fourth central springs 28-30 ofthe central bridge 12 undergo deformation, decoupling the mobile masses11A, 11B from the frame elements 31-33, which are thus fixed along Z.Instead, the first and second bars 25, 26 may rotate about the secondsymmetry axis S2.

In one embodiment, during movement of the mobile masses 11A, 11B, thefirst springs 27 act so as to prevent onset of a spurious vibration modeat about the operating frequencies. In fact, without the first springs27, the mobile masses 11A, 11B would be free to translate upwards(direction Y) indifferently in phase (non-desired movement for thegyroscope) or in phase opposition (desired movement for the gyroscope),causing onset of problems in driving the gyroscope 10. Further, due tothe presence of the first springs 27, the displacement of the first bars25 during Y movement of the mobile masses 11 decreases drastically(practically going to zero). Consequently, with the structure shown inFIG. 5, the modal mass involved in the Y movement is not modified, andthus there are no undesired reductions of the mass coupling factor viathe Coriolis force (“angular gain”) and thus of sensitivity of thegyroscope 10. In this way, the mobile masses 11A, 11B have three degreesof freedom (3 d.o.f.), uncoupled from each other, and the frame elements31-33 have just one degree of freedom (1 d.o.f.). Further, the first andsecond bars 25, 26 may perform a main movement according to a firstdegree of freedom (rotation about the second symmetry axis S2), and thesecond bar 26 also has a second degree of freedom (rotation about thevertical axis O).

In the gyroscope 10, when the mobile masses 11A, 11B rotate at anangular velocity that is constant or variable in a negligible way in themeasurement interval, about at least one of the three axes X, Y, and Zand are driven according to the three-dimensional trajectories indicatedabove, they undergo a frequency variation as a result of the Coriolisforces acting along the Cartesian axes X, Y, and/or Z. As discussed andshown by Eqs. [5], this frequency variation may be detected via sensingelectrodes X, Y, and Z, which generate sensing signals with variablefrequency, due to the capacitive variations associated to thethree-dimensional motion of the mobile masses 11A, 11B. These sensingsignals may be supplied to a processing unit (not shown), generallyexternal to the die integrating the gyroscope 10 to calculate theexternal angular velocities.

The described gyroscope 10 consequently has two mobile masses 11A, 11Bthat may be controlled independently in the three directions X, Y, andZ, thus providing a triaxial gyroscope 10.

Further, the same structure may be exploited for providing an amplitudemodulated gyroscope driven, for example, along axis X through the firstframe elements 31 (movement according to the arrows 50A, 50B in FIG. 2)and sensing along axis Y (movement according to the arrows 52A, 52B inFIG. 3, yaw mode) or sensing along axis Z (movement according to thearrows 54A, 54B in FIG. 4, roll mode).

The gyroscope 10 may be implemented as shown in FIG. 5, as regards onequarter of the structure, by virtue of its symmetry with respect to thefirst and second symmetry axes S1, S2. In particular, FIG. 5 shows apossible implementation of the driving electrodes and of the X and Ysensing electrodes, in addition to tuning electrodes, as describedhereinafter.

Here, the frame elements 31-33 are formed by generally rectangularbodies housing openings accommodating driving electrodes, sensingelectrodes, and tuning electrodes.

In detail, the X frame elements 31A (and 31B, not visible) surround Xdriving electrodes (whereof only references 59A are shown), X sensingelectrodes (whereof only references 60A are shown), and X tuningelectrodes (whereof only references 61A are shown).

Likewise, Y driving electrodes (whereof only references 63A are shown),Y sensing electrodes (whereof only references 64A are shown), and Ytuning electrodes (whereof only references 65A are shown) extend withinthe Y frame elements 32A (and 32B, 33A and 33B, not visible)

The X and Y driving electrodes 59, 63 and the X and Y sensing electrodes60, 64 are formed, in a known way, as projections of semiconductormaterial, extending from the substrate 15 (not visible in FIG. 5) withinthe respective X and Y frame elements 31, 32 (and 33, not visible) andthus capacitively coupled to the internal vertical walls of the X and Yframe elements 31, 32-33. They thus form parallel plate electrodesallowing an in-plane motion of the gyroscope 10.

FIG. 5 also shows stopper structures 77, formed in correspondingopenings of the X frame elements 31.

FIG. 5 shows possible implementations of the first, second, third, andfourth central springs 27-30, of the anchoring springs 36-38, and of thedecoupling springs 41-43. These springs are represented at an enlargedscale also in FIGS. 6-7 allowing appreciation of the variousconfigurations that determine their elastic properties selectively inthe X, Y, and Z movement directions of the mobile masses 11A, 11B. Inparticular, the second central springs 28 (whereof FIG. 5 only shows theone close to the first Y frame elements 32A, 32B and FIG. 8 only showsthe one close to the second Y frame elements 33A, 33B) are symmetricalonly with respect to the first symmetry axis S1, even though it ispossible to obtain a symmetrical configuration also with respect to thesecond symmetry axis S2. In general, even though the structure has ahigh symmetry, minor deviations from complete symmetry are possible.Further, in the embodiment of FIG. 5, further central springs 72 extendwithin the first bars 25, parallel to the second symmetry axis S2, andcouple the first bars 25 to further anchoring elements 73. The furthercentral springs 72 also enable the movements described above of thefirst bars 25.

FIG. 5 further shows the Z driving electrodes 68 with dashed line. Inaddition, FIG. 5 also shows Z sensing electrodes 69 and Z tuningelectrodes 70 with dashed line. All the Z electrodes 68, 69 and 70 arehere made as shown in FIG. 4, integrated in the substrate 15 and formedby appropriately insulated doped areas.

It should be noted that, in the embodiment of the gyroscope shown inFIG. 5, the dimensions of the electrodes 59-61, 63-65, and 68-70 arepurely indicative, and their effective size depends upon the desiredperformance. Further, the X and Y tuning electrodes 61, 65 could beomitted so as to leave more space for the sensing electrodes and thusimprove the performance of the gyroscope 10 as regards noise.

In this way, the present gyroscope is able to detect rotationalvelocities about three axes using only two mobile masses. The describedgyroscope thus has a reduced bulk and lower costs.

The present gyroscope is particularly reliable since it is potentiallyable to reject external accelerations in all directions with just twomobile masses.

Given its differential structure, the present gyroscope reduces theeffects of thermal stresses and increases the linear range ofsensitivity.

The present gyroscope may be obtained by surface processing techniquesusing a single structural layer of a uniform thickness (in a directionparallel to axis Z). Its production is thus very simple and compatiblewith current surface micromachining processes. The present gyroscopethus presents a high reliability and yield.

It is able to work both as triaxial gyroscope and as biaxial gyroscope(pitch-roll, yaw-roll, yaw-pitch), allowing good decoupling between themodes.

FIG. 9 illustrates a portion of an electronic system 400 thatincorporates the gyroscope 10 and may be used in apparatuses such as apalmtop computer (personal digital assistant, PDA), a laptop or portablecomputer, possibly with wireless capacity, a cellphone, a messagingdevice, a digital music player, a digital camera, or other apparatusesdesigned to process, store, transmit, or receive information. Forexample, the gyroscope 10 may be used in a digital camera to detectmovements and implement an image stabilization. In a possibleembodiment, the gyroscope 10 is included in a motion-activated userinterface for computers or consoles for videogames. In a furtherembodiment, the gyroscope 10 is incorporated in a satellite-navigationdevice and is used for temporary tracking of position in the case ofloss of the satellite-positioning signal.

The electronic system 400 of FIG. 9 comprises a control unit 410, aninput/output (I/O) unit 420 (for example, a keypad or a display), thegyroscope 10, a wireless interface 440, and a memory 460, of a volatileor non-volatile type, coupled together through a bus 450. Alternatively,the memory 460 may be internal to the control unit 410 and store theparameters and quantities for operating the gyroscope 10, such as thedriving voltages. In one embodiment, a battery 480 may be used forsupplying the system 400. The electronic system 400 may, however,comprise only some of the units shown in FIG. 9.

The control unit 410 may comprise, for example, one or moremicroprocessors, microcontrollers, and the like. The I/O unit 420 may beused for generating a message. The electronic system 400 may use thewireless interface 440 to transmit and receive messages to and from awireless communication network (not shown) with a radiofrequency (RF)signal. Examples of wireless interface may comprise an antenna, awireless transceiver, such as a dipole antenna, even though the scope ofthe present disclosure is not limited thereto. Further, the I/O unit 420may supply a voltage representing the stored information either as adigital output (if digital information has been stored) or as an analogoutput (if analog information has been stored).

Finally, it is clear that modifications and variations may be made tothe gyroscope described and illustrated herein, without therebydeparting from the scope of the present disclosure, as defined in theattached claims.

For example, the X and Y driving electrodes 59, 63 and the X and Ysensing electrodes 60, 64 may be formed differently from FIG. 5. Inparticular, instead of being formed as parallel-plate electrodes, theymay be comb-fingered electrodes, as shown in FIG. 10 as regards half ofthe Y frame element 32A and of the X frame element 31A. In particular,with this configuration, the X and Y frame elements 31, 32 have aplurality of mobile fingers 80 extending from the long sides of the Xand Y frame elements 31, 32, parallel to each other and directedinwards, comb-fingered with fixed fingers 81, formed within the X and Yframe elements 31, 32. The fixed fingers 81 are arranged parallel toeach other and to the mobile fingers and are anchored to the substrate(not shown), analogously to known comb-fingered structures.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A MEMS triaxial gyroscope, comprising: asubstrate; a first mobile and a second mobile mass suspended over thesubstrate; first, second, third, fourth, fifth, and sixth elasticelements; a first driving electrode structure that includes: a firstdriving body coupled to the first mobile mass through the first elasticelements; a first driving element coupled to the first driving body; asecond driving electrode structure that includes: a second driving bodycoupled to the second mobile mass through the second elastic elements; asecond driving element coupled to the second driving body, the first andsecond mobile masses being between the first and second drivingelectrode structures; a third driving electrode structure that includes:a third driving body coupled to the first mobile mass through the thirdelastic elements; a third driving element coupled to the third drivingbody; a fourth driving electrode structure that includes: a fourthdriving body coupled to the second mobile mass through the fourthelastic elements; a fourth driving element coupled to the fourth drivingbody, the first mobile mass being positioned between the third andfourth driving electrode structures; a fifth driving electrode structurethat includes: a fifth driving body coupled to the second mobile massthrough the fifth elastic elements; a fifth driving element coupled tothe fifth driving body; a sixth driving electrode structure thatincludes: a sixth driving body coupled to the second mobile mass throughthe sixth elastic elements; a sixth driving element coupled to the sixthdriving body, the second mobile mass being positioned between the fifthand sixth driving electrode structures; seventh and eighth drivingelectrodes structures in the substrate and coupled to the first andsecond mobile masses, the first mobile mass being over the seventhdriving electrode structure and the second mobile mass being over theeighth driving electrode structure.
 2. The gyroscope according to claim1 wherein the first and second elastic elements are rigid in a firstdirection and compliant in a second direction transverse to the firstdirection, the third and fourth elastic elements are rigid in the seconddirection and compliant in the first direction, a third direction istransverse to the first and second directions, the first and secondelastic elements are compliant in the second and third directions, andthe second and third elastic elements are compliant in the first andthird directions.
 3. The gyroscope according to claim 2, furthercomprising: a rigid supporting structure; first suspension elementscoupled to the rigid supporting structure and to the first driving body;second suspension elements coupled to the rigid supporting structure andto the second driving body; third suspension elements coupled to therigid supporting structure and to the third driving body; and fourthsuspension elements coupled to the supporting structure and to thefourth driving body, the first and second suspension elements beingcompliant in the first direction and rigid in the second and thirddirections, and the third and fourth suspension elements being compliantin the second direction and rigid in the first and third directions. 4.The gyroscope according to claim 2, further comprising a centralsuspension structure arranged between the first and second mobile massesand coupling the first and second mobile masses to the substrate.
 5. Thegyroscope according to claim 4 wherein the central suspension structurecomprises a cross-shaped element including a first bar element and asecond bar element, the first bar element extending between the firstand second mobile masses parallel to the second direction and havingportions coupled to the substrate through first elastic springsconfigured to enable rotation of the cross-shaped element at least aboutthe second direction, the second bar element extending in a directiontransverse to the first bar element parallel to the first direction andhaving a first portion and a second portion coupled to the first andsecond mobile masses, respectively, through second elastic springsconfigured to enable a translation of the first and second mobile massesin phase opposition in the first, second, and third directions.
 6. Thegyroscope according to claim 2 wherein the mobile masses have agenerally rectangular area and are arranged near each other on a firstside, and wherein the first driving body is arranged on a second side,opposite to the first side, of the first mobile mass, the second drivingbody is arranged on a second side, opposite to the first side, of thesecond mobile mass, the third driving body is arranged on a third side,transverse to the first side, of the first mobile mass, and the fourthdriving body is arranged on a third side, transverse to the first side,of the second mobile mass, the fifth and sixth driving body, the fifthdriving body being arranged on a fourth side, opposite to the thirdside, of the first mobile mass, the sixth driving body being arranged ona fourth side, opposite to the third side, of the second mobile mass,the fifth and sixth driving bodies being coupled to the first and secondmobile masses, respectively, through fifth and sixth elastic elementsrigid in the second direction and compliant in the first and thirddirections.
 7. The gyroscope according to claim 6 wherein the first,second, third, fourth, fifth, and sixth driving bodies comprise arespective rigid frame element, surrounding respective drivingelectrodes and in-plane, parallel-plate capacitive driving elements thatinclude the respective driving electrodes.
 8. The gyroscope according toclaim 7 further comprising in-plane, parallel-plate, capacitive sensingelements that include the frame elements of the first, second, third,fourth, fifth, and sixth driving bodies that surround respective sensingelectrodes.
 9. The gyroscope according to claim 7, further comprisingin-plane, parallel-plate, capacitive sensing elements that include theframe elements of the first, second, third, fourth, fifth and sixthdriving bodies surrounding respective tuning electrodes.
 10. Thegyroscope according to claim 6, further comprising: a rigid frameelement that includes the first, second, third, fourth, fifth, and sixthdriving bodies; and an in-plane, comb-fingered, capacitive drivingelements that includes a respective plurality of mobile fingerscomb-fingered to a respective plurality of fixed fingers.
 11. Thegyroscope according to claim 1 wherein out-of-plane, variable-distance,capacitive driving elements include the respective first and secondmobile masses and the seventh and eighth driving electrodes structures.